How Steam and Sun Can Light Your Life

In 1982, with a U.S. degree in biochem, he was drawn once more to the Valley. His father was ill in Mexicali, and the economy had buoyed. He got a job in an agricultural laboratory in Brawley, testing the chemicals in ag soils and the deep-seated brine being brought up by the fledgling geothermal industry. “Man, we made money in that lab, left and right, running silicas, irons, you name it.” With reservoir research bubbling, Cabañas eventually became head chemist for San Diego Gas and Electric’s only foray into geothermal energy, a small experimental plant, now an abandoned hulk (For Sale) down the road from Heber’s two plants. He worked for Magma Power Company at two projects in the East Mesa and since 1988 has worked at Ogden Geothermal, which earlier this year changed its name to Covanta.

In a spare office of a nondescript, well-insulated metal building, Cabañas recounts the history of the Valley’s geothermal plants, which, after decades of experimental development, became commercially viable in 1979. Engineers at first sent the fluid directly into a turbine, with limited success. Because the Imperial Valley geothermal brine is highly mineralized, silica (the most abundant mineral), calcium carbonate (the material of seashells), and other minerals stuck to the turbine blades as well as stuck to and clogged — like the buildup of plaque from bad cholesterol on our arterial walls — the well pipes themselves. Weighed down with gunk, the turbine blades eventually slowed and inevitably needed replacing.

Next, the geothermal industry developed “flash” technology, which is still employed at one of Heber’s plants. Flashing occurs when the highly pressurized hot water is brought up a production well and its pressure is suddenly lowered inside a separator, or flash tank. The lower pressure causes part of the water to flash, that is, to boil, or rapidly vaporize, and turn to steam. Routed into the turbine, the steam then drives the blades. Brine is often flashed twice. The first flash takes place in a high-pressure separator, and the second flash occurs in a low-pressure separator. After two cycles, called “dual-flash,” the spent brine is routed out of the plant and injected into the ground.

In 1993, Covanta decided to change one of its plants from a flash system to a binary, or heat-exchange, system and contracted Ormat, an Israeli company, to build the new operation. Binary technology provides greater efficiency than flashing. Now, instead of flashing the brine, the process transfers, or exchanges, the heat from the brine to another liquid, isopentane, which, at 82 degrees Fahrenheit, converts to a gas. The function recalls those standing steam radiators in old hotel rooms: Pipes full of hot brine heat the isopentane that flows around those pipes and then, as a gas, the isopentane is pulled through the turbine. There are two advantages to this new technology. One, the hot geothermal fluid can easily boil the isopentane. Two, the turbine blades, turned by the gas, do not corrode.

Covanta’s two plants — dual-flash and binary — are fed by 25 production wells. In a full-windowed room that looks onto the 12-acre dual-flash plant (the room is “decorated,” as geothermal engineers seem destined to do, with aerial photos of geothermal facilities), plant manager Byron Jensen says there is a 4000- to 6000-foot “optimal” range underground from which Covanta gets fluid at around 330 degrees. The original wells drilled by Chevron in the 1980s were deep — some down to 10,000 feet. Chevron drilled with “an oil-field mentality,” Jensen says. Mentality as in rapacious and random. Modern drilling technology is to go straight down or go straight down, then angle toward the source, termed directional drilling. The point is to go “as shallow as you can get away with,” Jensen says. For brine close to the surface, the company uses a slotted liner, a pipe with an angled cut at the bottom that sucks up fluid from only one point. “It’s cheaper, it’s faster, and it works better.” The other kind of pipe is perforated, that is, punctured with inch-wide holes. These holes allow fluid to leach in over less saturated expanses of the reservoir rock.

Because the land on top of the reservoir is 95 percent cultivated, engineers have perfected directional drilling. A whipstock bit permits a drill by minute turns to go in any direction. Later, to observe a directional well, Cabañas has my friend and me stand above one such well on an iron-grate platform. The heat wafts up in moiré patterns. Sun above and heat below, there’s no escape. Luckily these beefy pipes are wrapped with insulation like those pudgy blankets that enclose hot-water heaters. Hot is key. The higher the temp, the less the silica will crystallize. Cabañas reads from a metal plaque, fence-wire-tied to the fence: “This is Heber Geothermal Unit Number 7,” he says. “The total perforation [pipe punctured with inch-wide holes] is 5444 feet. At 3557 feet all the way to 5444 feet, the pipe is trying to pull in water. At 1137 feet the pipe starts going in a new direction,” angling toward its target. Before us is a temperature meter with a glass face and a dial. A needle quivers yet holds its point at 300 degrees.

Covanta’s computerized control room stands watch before the new 40-acre binary plant. Shift supervisor Jorge Nozot and control operator Manuel Mendoza monitor a bank of computers that display an elegant, neon-colored flow chart. The visual tracking system shows the heat-exchange system. The diagramming is complex, but the color coding helps us follow two routes. In red courses the ever-new brine, coming in, circulating, and being returned to the earth. In green runs the forever-cycling isopentane. Like Cabañas, Nozot reads the dial aloud: “We’re pulling in 15,000 gallons of fluid per minute from 11 production wells at 328 degrees Fahrenheit.”

Outside on a walking tour, we follow Mendoza as he hollers, points, waves us past the recycling, metamorphic journeys of fluid and gas. A geothermal plant resembles the dense circuitry of a silicon chip, but writ large. It is formally intoxicating, this terracing and tracking-back-upon-itself complexity of pipes and ducts, turbines and vents, pumps and tanks and smokestacks, in diameters from three inches to six feet, in harsh browns and harsher rusts. (Some readers know the 3D Pipes of Microsoft’s screen saver, an apt if hyperbolical depiction.) Pipes in the fields (we view them later on a driving tour) are simpler to grok. From multiple wellheads scattered over a two-mile radius, these pipes, some as large as tractor tires, run parallel to the Valley’s irrigation ditches. At Heber there are more than 50 miles of pipe, painted green where they pass through fields and brown where they hug dirt and paved roads.